In general, when automatic duplex printing is performed, the followings are important for the print result:
(1) Which of the front and back sides of discharged paper faces up?
(2) Can the user obtain an expected print result?
In conventional automatic duplex printing, for example, if a document of one page is printed in automatic duplex printing setting by erroneous user operation, printing is done in either fixed print mode depending on the printer driver: the print mode of duplex printing or the print mode of general single-side printing. Examples of printing in this case are as follows.
[Example of Printer Driver A]
When a document of one page is printed in automatic duplex printing setting, no paper sheet is discharged upon the completion of printing one page. The paper sheet is reversed via an automatic duplex unit, and then discharged. Compared to general single-side printing, the paper sheet is discharged onto the discharge tray with its front and back sides being reversed. An image process for printing that is executed in printing one page is one for duplex printing (the print density is slightly low (low quality) so as to prevent setoff).
<Advantage>
When a plurality of print jobs are printed at automatic duplex printing setting and contain a print job of one page, printed products are discharged onto the discharge tray with the image-bearing surfaces (which of the front and back sides faces up?) of all the printed products (discharged paper sheets) being unified.
<Disadvantage>
The print quality of 1-page printing becomes the quality (poor quality) of duplex printing.
[Example of Printer Driver B]
When a document of one page is printed in automatic duplex printing setting, printing is controlled to discharge a paper sheet through the same path as that of general single-side printing without the mediacy of the automatic duplex unit. An image process for 1-page printing is one for general single-side printing (high quality).
<Advantage>
The print quality of 1-page printing becomes the quality (high quality) of single-side printing.
<Disadvantage>
When a plurality of print jobs are printed in automatic duplex printing setting and contain a print job of one page, the orientation (which of the front and back sides faces up?) of a printed product for the print job of one page becomes opposite to those of the remaining print jobs. The printed products are discharged onto the discharge tray without unifying their image-bearing surfaces.
When a 1-page document is printed in automatic duplex printing setting, some applications output a blank page (no print image data) as the second page to the printer driver.
As a prior art, there is a technique as disclosed in Japanese Patent Registration No. 03380598.
In the former case of the prior art, a comparison between the example of printer driver A and that of printer driver B shows that each example has both a contradictory advantage and disadvantage. No optimal print result can always be obtained in all cases of automatic duplex printing. In some cases, the print result falls short of user's expectation, as described in the disadvantage.
In the latter case of the prior art, a print job of originally one page is processed as printing of two pages in which the second page is a blank page (no print image data). This results in a case as described in the disadvantage in the example of printer driver A. The print result falls short of user's expectation,